Update from chromium https://crrev.com/301315

sandbox/linux/bpf_dsl/bpf_dsl_forward.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SANDBOX_LINUX_BPF_DSL_BPF_DSL_FORWARD_H_
+#define SANDBOX_LINUX_BPF_DSL_BPF_DSL_FORWARD_H_
+
+#include "base/memory/ref_counted.h"
+#include "sandbox/sandbox_export.h"
+
+namespace sandbox {
+namespace bpf_dsl {
+
+// The bpf_dsl_forward.h header provides forward declarations for the
+// types defined in bpf_dsl.h. It's intended for use in user headers
+// that need to reference bpf_dsl types, but don't require definitions.
+
+namespace internal {
+class ResultExprImpl;
+class BoolExprImpl;
+}
+
+typedef scoped_refptr<const internal::ResultExprImpl> ResultExpr;
+typedef scoped_refptr<const internal::BoolExprImpl> BoolExpr;
+
+template <typename T>
+class Arg;
+
+class Elser;
+
+template <typename T>
+class Caser;
+
+}  // namespace bpf_dsl
+}  // namespace sandbox
+
+extern template class SANDBOX_EXPORT
+    scoped_refptr<const sandbox::bpf_dsl::internal::BoolExprImpl>;
+extern template class SANDBOX_EXPORT
+    scoped_refptr<const sandbox::bpf_dsl::internal::ResultExprImpl>;
+
+#endif  // SANDBOX_LINUX_BPF_DSL_BPF_DSL_FORWARD_H_